DE2136919A1 - Aqueous solution for etching copper - Google Patents

Description

Shipley Company, Ine,

2300 Washington Street
Newton, Massachusetts / V.St.A.

Our reference: S 2637

Aqueous solution for etching copper

1. Introduction ■

The invention relates to etching solutions and in particular continuously reusable etching solutions for copper ,, metals, the cupric ions as the primary oxidizing agent and a non-smoking complexing gown for the cupric ions.

2. State of the art

Stripping copper plating from substrates is; common practice in technology. Typical methods for | Stripping copper consist in the use of ' acidic ferric chloride, cupric chloride or chromic acid; solutions. While these methods are effective, they are often impractical where waste recovery is legal regulated i3t, since such solutions often have to be dealt with at considerable expense ^ before the used solutions can be discarded.

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ORIGINAL INSPECTED

Ferric chloride solutions typically contain ferric acid from about 28 ° to 42 ° Baume and free acid as a result of the hydrolysis of ferric chloride in aqueous solution, which results in a relatively low pH value, usually below 2.0. Cuprichloride etching solutions are usually 1 to 3 molar of cupricliloride and contain HGl, NaCl or NH, Cl as additives. As with the ferric chloride solutions usually have a pH value below about 2.0.

There are problems with most commercially available caustic agents connected. The ferric chloride and cupric chloride etchants described above attack Lötbleoh. All offer problems with regard to their destruction, since they are highly corrosive and, furthermore, the metals, in particular Copper, in solution the one required for wastewater destruction Disrupt bacterial activity and destroy plants and fish if they are in natural water be drained. In addition, the recovery of ~ dissolved or precipitated metals is not economical, although the value of the reclaimed metal would mean a profit.

There are αμοη alkaline etchants known above pH 8.5 and usually above 9.0 can be used. Such an alkaline caustic agent for Dissolving or stripping copper metal j st in the United States patent 3 231 503 and contains a chlorite, 3.B, sodium chlorite, as an oxidizing agent in one an ammonium salt as a complexing agent for the stripped metal containing alkaline solution. These Solution is used at pH 8-13 and preferably above pH 9. In this patent specification

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also said that the useful life of the solution after consumption of the primary oxidizing agent, i.e. the chlorite, can be extended by adding the Temperature with the use of dissolved copper in the cupric state as a secondary oxidizing agent Further dissolution of copper is increased, whereby during the process Cupri-ions are converted into Cupro-ions will. At this stage of the etching process, the etching solution consists of an ammoniacal chloride solution of cupric ions as the only oxidizing agent with a pH value between about 9 and 13. The chloride ions are supplied by the reduction of the chlorite ions.

It has been found that the use of ammoniacal caustic solutions, as mentioned in the above US Pat. No. 3,231,503, presents difficulties because of the high pH required causes excessive smoking of ammonia, whereby these vapors are harmful to the health of the operating staff and require expensive exhaust systems. Also, as a result of the leakage of ammonia from new ammonia may be added to the system if the solution is to be used for an extended period of time.

Description of the invention

The invention creates a new caustic agent that many the above-mentioned difficulties are eliminated. The etchant of the present invention is essentially one non-ammoniacal, non-smoking cupri caustic solution for copper metals, which in a preferred embodiment operates at a neutral pH of about 7.

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'/ 1 7 ρ q 1

The caustic contains a source of Gupri ions «, at least one non-smokingcles lsoniplsxfcilaend.es means, which form a soluble copper (II) complex '"in the solution can and preferably be a source of ghloriä- or bromide ions.

A major advantage of caustic invention is avoiding excessive ammonia fumes during Aetzensj, thus eliminating the need for expensive exhaust systems no longer "Sin Another significant advantage of the invention" ordered flaring _daß it almost unnecessary is "constantly fresh Apnoniumhydroxid sum Ez * 3 & t-z of

"Öei - to refill the known ammonia solutions which have escaped by evaporation. Another advantage is that the pH value does not have to be kept above 8 _s 0 or below 2 _S 0 in order to achieve an effective Aetsuiig su, as is the case with the" known solutions of the 3? all is § rather it can be chosen within a relatively wide range, preferably from 4 and 13? 3® according to a choice of the koiaplex-forming agent and its solubility properties at a given pH value respect that the etchant a aeutralen at _a pH-value / is a major advantage of the invention "verv sndbar, the below. as av / isehen about β and 3 and preferably between about TpO and 7 ^ 8 schv / ankend is given.

The use of the etching solutions according to the invention "also brings certain components with you. For example the niclit-smoking complexing agents more expensive than ammonia. However, these extra costs are compensated for by the fact that no refilling is required is and that the etchant according to the invention is ongoing

reusable sln & ₉ as it is "described" in more detail below. Also, some caustic agents according to the invention have a somewhat slower caustic rate than the ammoniacal caustic agents described above acts and the etching rate increased significantly ₈ so that it is reached that of the known ammoniacal etching solutions and in some cases even "Ss exceeds noted _s that in this embodiment, the ammonia is added only in small quantities and, consequently, a smoking of ammonia does not substantially dimensions takes place "so that an exhaust system is not required is kept _o in the preferred embodiment ₉ wherein the pH = ¥ ert below about 8.0, no ammonia fumes are detectable during the cauterization

In a further embodiment of the invention Hitrate ions are added to the solution, which increases the capacity Improve this etchant for ongoing use without refilling or regeneration

The caustic agents described above can in principle be reused on an ongoing basis, provided that the copper deposit is removed continuously or periodically during the etching process. It has been observed that forms the continuous Aetsen on the surface of a copper part to be etched, a film, which slows the etch rate, to in some cases, the etching stopped In this embodiment of the invention the FiIm ₅ the most likely a film of copper deposition

18 6 0

β -

is j, through. Addition of a small amount of nitrate ions to the caustic solution removed »

In another embodiment of the invention there are a molybdenum which is soluble in the solution is added to the acetal solution. Tungsten or yanadine compound to which then

. an attack of a tin or lead-tin solder mask almost completely prevented.

Description of the preferred embodiments

The etching takes place according to the following two reactions from ι

Cu ⁰ + Cu * ⁺ --—> 2 Cu * ^{2 Cu +} ° 2 ^ 2 Cu ⁺⁺

As stated above, 1 mole of divalent copper oxidizes 1 mole of metallic copper to 2 moles of monovalent copper, which is then oxidized with atmospheric oxygen to divalent copper, for example by bubbling air through the solution, by spraying 7er- ψ ' etching or the like. Bivalent copper, which is sufficient for a satisfactory etching of copper and acts as an oxidizing agent, is kept permanently in solution by the salifying effect of the complexing agent, while excess copper precipitates in the form of an oxide or hydroxide. In this way, the etchant is not saturated with copper residues. With periodic or continuous removal of the copper deposit as it is formed, this can be

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Caustics used continuously ^ = vorausge that certain forsiehtsmaßnahmen setztj be taken "wirdo er3.äutert in more detail below, it is believed that _s chloride or bromide ions are in the solution as a catalyst or promoter for the etching reaction,"

Almost every cupric salt can be used as a source for the cupric ions. Typical Cuprisalze are "for example Cuprisulfats Cuprichlorid ₅ Guprinitrat ₅ Cupriacetat und dergl" The amount of Gupri ions contained in the caustic solution is not critical, can vary within wide limits and depends to a certain degree on the amount ^ of the coaiplexing agent used al) ο A "preferred range is between about OpI and I ₅ 2 mol per liter of solution at the beginning and best between 0 _s 2 and 0.6 mol per liter." Higher concentrations tend to increase the rate of the oxygen

The komplesbilaenäe agent of the invention fulfills an important ZweckJ you niraat as ₅ dai it "Sun ^ riel brings copper into solution äaB take place Aetsnag kaxm _a This Note's looking _s DAB within the applicable pH range of 4-15? Not enough Gupri ions are kept in solution in order to give a sufficient rate of etching.If the concentration is increased above the normal solubility limit by using a complexing agent, so much I can be added that a sufficient etching rate is achieved, which is suitable for the purposes according to the invention at at least 0.1 mil copper per minute. while stirring the solution.

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The choice of complexing agent is not important provided certain guidelines are followed. For example, the complexing agent must not smoke, ie it must not develop any noticeable ammonia vapors during the etching process. As a result, ammonium hydroxide as a complexing agent does not fall within the scope of the invention, although ammonium ions are known to be added in smaller amounts as promoters, as will be described in more detail below. Another condition for the complexing agent is that it can form a solution-soluble copper (II) complex at a pH within the range of 4 to 13 within which the caustic agent can be used. Furthermore, the copper (II) complex should dissociate in the solution to such an extent that etching of copper at a minimum rate of 0.1 mil per hour is possible. In this connection it is easy to see that the degree of dissociation of a complex depends on numerous factors, for example the pH of the solution, the temperature of the ib'sungg, the concentrations of various additives and the like Group of process conditions does not dissociate sufficiently, while under another group of process conditions it dissociates while achieving a satisfactory etching rate. Merely as a guideline, it is stated that the logarithm of the stability constant (K ₁ ) for a specific copper (II) complex should not exceed 18 and preferably 12 at 25 ° 0. Stability constants for a large number of copper (II) complexes are given in Martell, Stability Constants of Metal-Ion Complexes, Special Publication Ho. 17, Paragraph II, The Chemical Society, London, 1964, which is incorporated herein by reference.

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Typical complexing agents for the erfindungsgemäßea purposes are, for example, hydroxycarboxylic acids, in particular aliphatic hydroxycarboxylic ,, such as glycolic acid _s apple = acid, tartaric acid, gluconic _s lactic acid and the like ₀ J polyalcohols such as glycerin "sorbitol ₉ diethylene glycol and mannitol ι ketonic ₅ Z ₀ B ₀ pyruvic acid and levulinic acid ι ^ polyamines polyamines such as in particular aliphatic Triaethjlamini, Tetrahydroxypropylaethylendiamin, Pentahydroxypropyldiaethylentriamin and Propylendiamin5 hetero "aliphatic dicarboxylic acids, S ₀ B ₀ Diglykolsäurep amino acids ,, especially aliphatic amino acids such as aminoacetic acid ;, _B alpha-aminopropionic _s beta-Aminopropionsäurej, alpha = aminobutyric acid , Iminodiacetic acid _p iminodiacetic acid. and Aethylendiaminotetraessigsäures alkanolamines "as Monoaethanolaminj, diethanolamine _s Monoisopropanolamine and diisopropanolamine and Pyrophosphate _s s _o b _o sodium and Kaliumpyrophosphatc Among the above certain alkanolamines are most preferred because they yield the highest Aetzgeschv / indigkeiten and alkylene amines are preferred the least, It should be noted that the logarithm of the stability constant for typical alkylene amines is significantly higher than for typical alkanolamines, which to a certain extent confirms the theory explained above regarding the dissociation of the copper (II) complex "

Although lower amounts may be used to complex forming agents in solution, xvird but preferably an amount used is sufficient to the total, at the beginning in the solution contained cupric ~ ion complex to bind and in particular, the complex-forming agent in an amount of at least 1.5 times the amount present,

109386/1 SSO

which is to complex with all originally in the solution containing cupric ions is required and am "Best" is the amount at least 5 times the amount required Amount to achieve a good etchability. As will be apparent to those skilled in the art, the concentration depends of the complexing agent used, of the type between the complexing agent and the Cupric ion formed from ligands, i.e. whether the ligand is one-toothed, two-toothed, three-toothed or the like.

That. Ammonium ion is not required for the action of the caustic agents according to the invention, although it is expedient

"Adds an ammonium salt as it acts as a promoter for the Etching speed is used. Typical for the invention Ammonium salts suitable for purposes are ammonium carbonate, ammonium sulfate, ammonium chloride and the like. The amount of ammonium salt is not important and can be vary widely between 0 and less than the amount which causes noticeable smoke formation during etching would effect. The preferred range is between 0.5 moles per liter of solution and 5 moles per liter and preferably between about 1 and 2 moles per liter of solution. It should also be noted that when an ammonium salt is used will, even if doing so during continuous

fc caustic some ammonia is lost, a refill of ammonia is not required, since there is obviously an equilibrium at which no further equilibrium exists Ammonia is lost and therefore no ammonia needs to be added.

The chloride or bromide ion can be used in either the caustic solution in the form of cupric or ammonium chloride ·· or bromide or in any other suitable form such as sodium chloride or bromide. The function of the halide ion is not entirely clear, but one takes

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suggest that it increases the rate of etching by possibly acting as a solubilizing agent for monovalent copper formed on the surface of a copper part during etching. The chloride or bromide ion can be present in smaller quantities; its actual concentration is not critical. Preferably it is present in the solution in an amount of at least 0.1 moles per liter of solution and preferably from O ₉ 2 to moles per liter. It appears that there is a synergism between the ammonium ion and the halide xon which results in a considerable increase in the rates of etching.

The nitrate ion will _; the etch solution added to prevent ma the formation of "copper mud" su on the copper surface, which otherwise could affect the cauterization "Without being bound by theory, it is yet to _see that this film Oupro-containing copper and Mtrat-'Ion acts as a solubilizing agent for it »In addition, it is assumed that the Hitrat-Xonen. secondary oxidation of monovalent copper "assist in the bivalent © form. The source for the Witrat-Ieaea is not important. compounds such as ammonium nitrate ₅ nitric acid and alkali and alkaline earth ss.B _o latrinam- or potassium nitrate are suitable. Small amounts of litrat Ions have a less beneficial effect than larger amounts, until a maximum is reached beyond which no further improvement can be achieved wipe about 1 and 1.5 moles per liter of solution.

Soluble molybdenum, tungsten or vanadium salts can also be added to the etching solution to prevent attack

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can be added on a solder mask. When they are added this can be in the form of a water-soluble organic or inorganic salt, e.g. an alkali or Alkaline earth salt, in the form of an ammonium molybdate or the like. Or in any "any other form. The preferred forms are e.g. ammonium glybdate, molybdenum trioxide, Sodium tungstate, sodium vanadate and vanadium pentoxide. The amount of molybdenum, tungsten or vanadium added to the etchant is not critical; small amounts result in a lesser effect than larger amounts up to a maximum, beyond which no further Improvement is achieved. In general, the amount of molybdenum or vanadium, expressed as metal, can be vary between 0.005 and 0.20 moles per liter of caustic solution.

As indicated above, the caustic agents according to the invention can be used over a wide pH range, preferably from about 4-13 can be used. In the most preferred embodiment of the invention, however, the caustic agents are used within a relatively neutral pH range of about 6.0 to 6.8, and most preferably between about 7.0 and 7.8 because of the greater variety of complex-forming agents available, the lack of attack on substrate materials, Photo masks, Fötoaetzschutzschichten, because of the easier handling, security and the like. used. Working at neutral pH is believed to be unique as such, as it has been so far neutral caustic agents were not on the market at all.

The operating temperature for the caustic solution is not important. Satisfactory results are obtained between below Usual room temperature and the boiling point of the

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Etching agent, although it is generally expedient to use the Maintains temperature slightly above room temperature, preferably between about 38 and 71 ° C. At higher temperatures a faster etching speed is possible, thereby reducing the number of available for the purposes of the invention complexing agent is enlarged. The temperature limit used for etching appears Facility, since the etching agents are many commercially available Attack facilities at higher temperatures.

The etching agents according to the invention can be used continuously. In addition, they do not require regeneration or an essential refill because of the active ingredients are not consumed or lost, and bivalent copper is continually produced by the oxidation of etched Monovalent copper supplied and kept in solution in an approximately constant amount by the complexing agent will. When using ammonia as a promoter, some ammonia can be lost at first, it seems however, an equilibrium can be established by itself in which no further ammonia is lost and none Addition of ammonia is required. Therefore no further ammonium salt needs to be added. The tolumen the caustic agent is kept constant by adding water.

I ^{1 For} continuous etching operation, precipitated copper must be removed either continuously or periodically during the use of the etching agent in order to prevent it from becoming saturated. This can easily be done by the person skilled in the art by circulating part of the etchant through a filter system, a centrifuge or other

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"take place in a known manner. Da3 copper obtained in this way" is located likely in the form of a hydroxide which is still of "considerable commercial value. For example, the precipitate can be used to produce a fresh oil solution.

The following are examples of the invention, in which the etching is carried out in a calm solution will. Few possible modifications are specifically mentioned, but the invention is not limited to its scope limited examples. Moving the solution "" naturally accelerates the reaction rates mentioned. In this regard, spray etching is very preferred over etching in a calm solution, since the speed is 5 to 30 times greater. In all cases, ventilation of some kind is required to convert monovalent to divalent copper necessary.

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Examples 1 - 12

Ingredient (g / l) 1 2 3 4th ■ 5 6th 7th 8th 9 10 11 12th - 200 Cuprichloride
Diliydrate 50 50 50 50 50 50 50 50 50 50 50 Cupric sulfate
Pentahydrate 50 Monoethanolamine 200 200 200 200 Diisopropanolamine 200 Tetrahydroxypropyl-.
ae thy lend i aiain
ι 200 - Tartaric acid 200 200 Malic acid 135 100 Trihydroxydi-
acetic acid 160 G-lycolic acid 200 7.4 Sodium chloride 25th 25th 7.0 Ammonium chloride 50 50 50 50 75 75 50 60 o, 35 Ammonium nitrate 50 50 50 50 50 50 50 80 pH (1) x 7.5 7.6 7.5 7.4 7.5 6.6 7.5 7.5 7.5 7.5 7.6 pH (2) 7.5
Etching speed o, 22 7.2 7.5 7.1 7.3 6.6 7.2 7.2 7.1 7.3 7.2 ! temperature ° 0 52 o, 28 o, 16 o, 14 0.12 o, 14 0.28 0.26 o, 17 o, o3 o, 4o 52 52 52 52 52 52 52 52 52 80

(l) Starting pH of the solution was either adjusted with hydrochloric acid or Sodium hydroxide adjusted to the specified value.

(2) The pH was after at least 20 minutes of operation and after measured after standing for at least 8 hours

(3) The etching speed is in mils per minute of etched copper when using a copper foil with dimensions τοη 5 χ 5 cm given in 1 liter of caustic

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In the preceding examples, no ammonia vapors were detectable during use of the caustic agent and only a slight ammonia odor was detected during the preparation of the caustic agent. The proportionate The slow etching rate of Example 10 is probably due to the absence of chloride ions attributable to.

A loto mesh coat was clad on top of a copper clad Layered structure applied and this was immersed in the etchant according to the preceding examples. There was no effect of the etching agent on the anti-etching protective layer established.

Examples 13-18

Components 13th 14th 15th 16 17th 18th Cuprichloride
Dihydrate 50 50 50 50 50 50 Monoethanol
amine 150 150 150 Tartaric acid 200 200 200 200 200 200 Ammonium-
chloride 50 50 50 50 50 50 ammonium
nitrate 50 50 50 50 50 50 pH. (1)
pH (2) 5.0
5.2 6.5
6.6 7.5
7.3 9.2
7.8 11
8.2 13th
9.3 Etching speed
age (3)
O
Temperature C 0.14
52 0.13
52 0.14
52 0.22
52 0.20
52 0.30
52

(l), (2) and (3) as above

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At low pH, i.e. "at about 8.5 and below, no ammonia vapors were detected. At higher pH was assumed to be an ammonia odor, but in no case was the odor so strong as to protect an exhaust device was required by the operating personnel.

Example 19 Example 20 Cuprichloride dihydrate 40 g 40 g Monoethanolamine 120 g_ '150 g Ammonium nitrate 100 g - Sodium nitrate - 75 g Ammonium chloride 70 g Sodium chloride 75 g Waxer on 1 offender to 1 liter PH 7.8 7.5 temperature 52 ° C 52 ° C

The above compositions were for a spray-etch as opposed to the dormant solutions as in Example 1-12 used. As a result of the ventilation occurring during spray etching, the etching rate was higher. For the solution of Example 19, etching proceeded until about 23 ounces of copper per gallon of etchant were resolved. Compartment slowed down 23 ounces of worn copper the etching as a result of the formation of a precipitate. This precipitate was filtered off and the etching was repeated. During about the same time, it was able to produce about 22 ounces of copper per gallon

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to be irritated. Regarding the composition of Example 20 etched for about 25 minutes, during which time about 9 ounces per gallon of solution etched became. The precipitate was filtered off from the solution and the etching was repeated - both compositions of Examples 19 and 20 can be used continuously.

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Examples 2.1 - 4 <

Ingredients (g / l) 21 22nd 23 24 25th 26th 27 28 29 30th Cuprichloride
Dihydrate 50 50 50 50 50 50 50 50 50 50 Monoethanolamine 200 200 200 200 200 200 200 Tartaric acid 200 200 200 Ammonium chloride 50 50 50 50 50 50 50 50 50 50 Ammonium nitrate 25th 25th 25th Molybdic acid 15th Sodium tungstate ' 25th 25th Sodium vanadate 25th Vanadium pentoxide 10 pH ^(l) 7.5 7.5 7 _; 5 7.5 7.5 7.5 9.2 7.5 7.5 ' 7.5 Effect ^ IT-27 ^ 100 50 50 70 O 25th »1 ° 100 75 70 brazing sheet ^ 100 10 ■ 20 50 ' 10 50 0 - 50 20th 20th Tinplate ^ 100 10 20th 10 10 25th 0 60 10 10 LT-27 ^ 20 0 - 0 0 - - 100 50 5 Solder sheet ^ 5Od
Tinplate ^ 100 0
0 0
10 Od
0 - 50od
50 Od "
10 0
5

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Examples 21-40 (continued)

Ingredients (g / l) 31 32 33 34 35 36 37 38 39 40 Cuprichloride
Dihydrate 50
Monoethanolamine
Tartaric acid 200
Ammonium chloride 50
Ammonium nitrate 100
Ammonium molybdenum
Molybdic acid
lia tr iumwo 1 fr ama t
I Sodium Vanadate 25
Vanadium pentoxide 50
200
50
100
25th 50
200
50
100
25th 50
200
50
100
25th 50
200
5Ö
100
25th 50
200
50
100
25th 50
200
50
100
25 ' 50
50
100 50
50
100
25th 50
•
100
100
25th PH ⁽¹⁾ 7.5 5.0 9.4 5.0 9.3 5.0 9.3 8.5 8.5 9.0 Effect ^
LT-27 ^ '75
Solder sheet ^ Od
Tinplate ^ 0
LT-27 ⁽³⁾ 50
Solder sheet ^ Od
Tinplate ^ Od 80
70
2Od O
1Od
O 50od O
I CM I I I I 70 Od 25th
25th
25th
15th
25th
25th O Ul O O O O O
O
O
5
5
O

(1) Starting pH of the solution, to the specified value adjusted with either hydrochloric acid or sodium hydroxide.

(2) The effect of the Peststellung Aotzmittels samples were immersed with the specified tin or lead-tin alloy for 5 minutes in a bath maintained at 52 ^U C etchant. The results are given as a percentage of the plating destroyed (heavily etched) of the surface. The letter "d" indicates that the panel was discolored. The first three numbers per example in the "Effect" column show the effect in a fresh solution, while the last three values show the effect of a solution that has already dissolved 6 ounces of copper per gallon.

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(3) LT-27 means that the sample is made of a dip coating Owns tin.

(4) "brazing sheet" means an electroplated tin-lead alloy, which contains approximately equal amounts of both metals.

(5) "Tinplate" means electroplated tin.

From the foregoing it can be seen that the added molybdenum, vanadium and tungsten cause the attack Tin and tinned lead plating decreased in all cases, although the effect is not the same in all cases, adding some examples a much greater improvement show than others.

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Claims (15)

Claims Containing neutral aqueous caustic solution for copper a source of cupric ions as an oxidizer for copper and a non-smoking complexing agent for the copper ions, which form a soluble copper (II) complex in the solution at the pH of the solution • which dissociates in the solution under the operating conditions to such an extent that copper at a speed is etched at least 0.1 mils per minute. 2. etching solution according to claim 1, characterized in that "it acts as a promoter chloride ions, bromide ions and / or Contains ammonium ions. 3. etching solution according to claim 2, characterized in that ^η it still contains so much nitrate rlonen that the formation is prevented of a film on the copper surface during etching. 4. etching solution according to claim 2, characterized in that no matter how much molybdenum, tungsten and / or vanadium ions it contains that tin and tin / lead platings can attack is delayed significantly. 5. etching solution according to claim 2, characterized by a pH value between approximately 6 and 8. 6. etching solution according to claim 2, characterized by a pH value between about 7.0 and 7.8. 7. etching solution according to claim 2, characterized in that the cupric ions in the starting solution in an amount of 109886/1860 about 0.1 to 1.2 mol per liter are present and the complexing agent in at least one for complexing with all cupric ions a sufficient amount is present. 8. etching solution according to claim 2, containing chloride or Brcmide ions in an amount of 0.2 to 2.0 moles per liter Solution, molybdenum, - tungsten and vanadium in an amount of 0.005 to 2.0 moles per liter and nitrate ions in an amount of 0.2 to 2.5 moles per liter. 9 “Caustic solution according to claim 2, containing ammonium ions in an amount / from 0.5 to 5.0 moles per liter of solution. 10. etching solution according to claim 2, containing chloride ions in an amount of 0.2 to 2.0 mol per liter of solution and Ammonium ions in an amount of 0.5 to 5.0 moles per liter of solution. 11. etching solution according to claim 9, characterized in that the complexing agent is an alkylenamine, an alkanolamine, a hydroxycarboxylic acid, an aminocarboxylic acid, a polyalcohol, a polyamine, a heteroaliphatic Is dicarboxylic acid, an amino acid or a pyrophosphate. 12. etching solution according to claim 11, characterized in that the complexing agent is an alkanolamine. 13. Aqueous etching solution according to claims 1-3 and 4-12, characterized in that it has a pH between about 4 and 13. 109886/1860 14 · Application of the caustic solution of claim 1 to the continuous Etching of copper, including copper in the etching agent dissolved and a formed copper precipitate is removed so far that a saturation of the caustic solution with the precipitation is avoided. 15. Type of application according to claim 14 for the lcontinulicherj. Etching of copper using the etching solution according to claims 1, 2, 3 and 13. 199886/1860